Impact of prevalence of P. gingivalis and S. cristatus in oral health disparities Adult periodontitis is disproportionally distributed among races, and has a significantly higher incidence in African Americans (AA) compared to European Caucasians (EC), even when co-variants such as diabetes and other health and social factors have been taken into account. This proposal examines the potential role of two oral microbial biofilm components (P. gingivalis and S. cristatus) on this disparity. Titers to the oral pathogen P. gingivalis are reported to be higher in dentate subjects with, compared to those without periodontitis. Our laboratory was the first to report an intergeneric communication between S. cristatus and P. gingivalis. We identified a surface protein of S. cristatus, arginine deiminase (ArcA) that serves as a signal molecule to which P. gingivalis responds by repressing the expression of the fimA gene, which codes for the major subunit protein of long fimbriae. The latter is required for bacterial colonization of P. gingivalis and host cell invasion. Recently, we demonstrated that S. cristatus indeed inhibited colonization of P. gingivalis in the murine oral cavity and reduced periodontal bone loss in those mice tested. Therefore, we hypothesize that colonization of P. gingivalis is dependent upon the nature of the initial streptococcal biofilm, and that certain as yet unidentified risk factors of periodontitis are the driving force behind different streptococcal profiles of these initial microbial biofilms. We will first compare the prevalence of S. cristatus versus P. gingivalis in the oral cavities of periodontally healthy AAs, ECs and Mexican Americans (MA) versus those with periodontitis (before and after periodontal treatments). Our objective is to determine if there is a link between a lower prevalence ratio of oral S. cristatus:P. gingivalis in AAs, or MAs compared to ECs, which might help account for the higher risk of periodontitis in AAs and MAs. We will also then test the potential involvement of other periodontal risk factors in this disparity, and their role in the prevalence of S. cristatus versus P. gingivalis. Finally, we propose to investigate if intense education of periodontal health will promote a shift in ratio of S. cristatus versus P. gingivalis in periodontitis patients. We anticipate that the proposed studies will provide important information regarding the pathogenesis of periodontitis and the nature of the microbial biofilms found in different races/ethnics, and will pave the way for extended studies in future, focused on the development of appropriate interventional strategies targeted at eliminating of P. gingivalis colonization.